After screening a large series (n = 491) of asymptomatic males of infertile partnerships for chlamydial immunoglobulin (Ig) G antibodies (Chlam AB), no significant influence of past chlamydial infection was found with regard to semen analysis, postcoital testing, in vitro sperm-cervical mucus penetration tests with hormonally standardized cervical mucus, circulating antisperm antibodies (detected with three different methods), local IgG and IgA antibodies (detected by means of the mixed antiglobulin reaction test) on the sperm surface, the sperm-cervical mucus contact test, and a microbial screening of semen samples for mycoplasmas and other potentially pathogenic micro-organisms. However, when the findings were correlated with infertility factors of patients' female partners and the subsequent pregnancy rate in a prospective study, a significant positive correlation of male Chlam AB with a tubal factor in their wives as cause of the couple's infertility was found. The results suggest that the main influence of Chlamydia trachomatis on male fertility is based on sexual transmission and negative influence on tubal function of female partners, but not on reduced sperm functional capacity.